Concentrated brine-incoming feed vapor compression desalination system

ABSTRACT

A multistage flash distillation system wherein heated feed water is passed through successively lower stages to flash into vapor, which vapor is condensed as distillate, the effluent brine from the lowest stage being passed to a boiler to produce steam, which steam is compressed and so utilized to heat the incoming feed.

United States Patent [72] Inventor William Rodger Williamson 3,152,05310/1964 Lynam 202/173 Waterford, Conn. 3,288,685 11/1966 Kemper et a1203/24 X [21] Appl. No. 774,801 3,433,717 3/1969 Loebel 1 202/173 [22]Filed Nov. 12,1968 3,388,045 6/1968 Goeldner etal. 203/11 X [45]Patented Sept. 21,1971 3,489,652 1/1970 Williamson 203/11 [73] AssigneeAMF Incorporated 3,501,384 3/1970 Starmer 203/11 2,759,882 8/1956Worthen et a1. 203/24 X 3,305,455 2/1967 Loebel 202/173 X [5 1CONCENTRATED BRINE-INCOMING FEED 3,362,458 1/1968 Hopper 203/26 x VAPORCOMPRESSION DESALINATION SYSTEM 10 Claims, 2 Drawing Figs. 1 rzmaryExamrner-Norman Yudkoff Asszstan! Exammer David Edwards [52] US. Cl203/11, Anameys ceorge w p i and Murray Schaffer 202/173, 203/24, 203/26[51] 1nt.Cl 501d 3/06 Field Search 202/173 ABSTRACT: A multistage flashdistillation system wherein 23i203/11, 100 heated feed water is passedthrough successively lower stages 56 R f d to flash into vapor, whichvapor is condensed as distillate, the l 1 e erences I e effluent brinefrom the lowest stage being passed to a boiler to UNITED STATES PATENTSproduce steam, which steam is compressed and so utilized to 2,389,78911/1945 Latham 203/2 4 X heat the incoming feed.

36 I 250 F 3 229 COMPRESSOR D/FSEL "NW- W- a ENG/NE I45 /4C /4d A 229;44 465 -/6c 54 24\ HIRE/IVE a a 34 24/ F 2397 237 F Z BRINE 0U,

30 229"; W fi m) Z/7F 35F AAAAA /6 20 235 DIST/HATE OUT CONCENTRATEDBRINEJNCOMING FEED VAPOR COMPRESSION DESALINATION SYSTEM The presentinvention relates to the method and apparatus for distilling sea waterand producing fresh water therefrom.

The main object of the present invention is to provide a simple,economical evaporator of the multistage flash type in which the heattransferred to and found in the final distillate product is employed asa source for heating the incoming or raw salt water to evaporationtemperature It is another object to provide an evaporator of themultistage flash type in which the distillate vapor of the final stagesis employed to impart heat to the feed water entering the flash chamberof the first stage.

It is another object of this invention to provide an evaporator of themultistage flash type having characteristics of operation superior tothose presently in existence.

Another specific object of this invention is to provide evaporators inwhich the gained output ratios of operation are far superior to thosepresently obtainable. The gained output ratio being defined as the ratioof the amount of distillate produced to the amount of power (generallysteam) needed to produce such distillate. The amounts are generallystated in terms of pounds per hour (/hr.).

Briefly, the present method and apparatus comprises the compression ofdistillate vapor from the flash evaporation of brine exiting from thebottom or lowest end of a multistage cycle in which compressed vapor isemployed to power a sea feed heater imparting heat to the feed.

The system of the present invention eliminates a number of problemsgenerally associated with high economy distillation plants. First, fewerflash stages are required to effect total production, reducingcomplexity, cost and size of vessels. Subatmospheric stages areeliminated permitting the entire system to be operated at the moreefficient pressures above atmosphere. The present system eliminates theneed for highly sensitive control of interstage flow and thermalequilibrium since it is not necessary to maintain small temperature andpressure differentials between stages. Further, all evaporation stagesof the present device lie between the sea feed heater and the brinereboiler. Above all, the present method provides for a quantitative andqualitative drop in initial power (steam) required to operate thesystem. This gives rise to geometric increases in Gained Output Ratios(GOPR).

These advantages and objects as well as others will be seen from theaccompanying description in which reference is made to the appendeddrawing wherein:

FIG. 1 is a schematic view depicting one form of the present invention,and;

FIG. 2 is a schematic view ofa modified form of the present invention.

In FIG. 1, a multistage evaporator of the conventional type like that ofU.S. Pat. No. 3,186,924 is shown comprising a plurality of flashchambers l0a-l0d which operate at successively lower pressures andtemperatures proceeding from a high pressure stage a to the lowestpressure stage 10d. As heated sea water is introduced successively froma sea feed heater 12 into the flash chamber 10, a portion thereofflashes into vapor which passes into a heat recovery chamber 140-1411,respectively, through lines 160-1611. The condensed vapors are collectedfrom the condenser chambers and are removed by a distillate pump 18 toexit through line 20. Raw sea water feed makeup is delivered by line 22through an external heat supply, steam heat exchanger 24, whichconstitutes the sole source of power not inherent in the system. Theexternal heat source may be raw steam, turbine exhaust or any othersuitable and available heat source. The raw sea water then passes into aheat reject flash chamber or reboiler 26 where a portion flashes intovapor and the remainder passes into and comingles the effluent unflashedbrine exiting via pipe 28, from the flash chambers l0a-l0a'. A portionof the brine and raw sea feed is passed via pump 30 and line 32 to thecondenser coils of condensing chamber 14 to act as the condensing mediafor the vapor flashed in chambers l0a-l0d. The brine feed is then passedthrough heater 12 where it is heated and fed into flash chambers10a-10d.

A portion of the effluent brine from flash chambers l0a-10 is bled fromthe reboiler 26 and blown down via line 34.

The vapor formed in reboiler 26 from the effluent brine and the raw seafeed is completely compressed in compressor 36 and is fed via line 38 tothe heater 12 where it imparts its heat to the feed water. Thecompressed vapor condenses to liquid and passes into the collectingtrays of the condenser chambers to mix with the fluid and exit via line20.

The reboiler is a conventional flash device without condensing sectionattached. The compressor 36 is a conventional compressor of moderatesize and design sufficient only to compress the volume of vapor createdin the boiler so as to evaluate its temperature by approximatelyone-sixth-onetenth that of the temperature of the sea feed or brine inthe boiler.

Since the reboiler is outside the bottom end of the multistage systemits brine effluent is sufficiently cool to constitute proper coolingmedia for condensation without modification of the pressure-temperaturedifferentials of the stages l0a-l0bq. In accordance with establishedevaporation principles the flow of condensing fluid is countercurrent tothe flow of sea feed through the flash chambers.

As is the usual practice a distillate cooler or brine preheater 40 maybe provided to cool the blowdown exiting from line 34 and the distillatefrom line 20 while simultaneously preheating the raw sea water infeed.

Omission has been made here of the details concerning the structure ofthe individual stages and their linkage since such details are now quitecommonly known. Reference, however, may be made to the aforementionedU.S. Pat. No. 3,186,922 or to U.S. Pat. No. 3,399,118 and U.S. Pat.applications Ser. Nos. 6l5,743, 615,572 and 440,493, all in the name ofthe present inventor, now U.S. Pat. Nos. 3,513,075; 3,489,650; and3,418,213, respectively.

A typical operating scheme as a shipboard evaporator is depicted in FIG.1 which will be employed to illustrate the operative advantages of thepresent invention. Raw sea water, at ambient temperatures which in mostlatitudes approximates F., is fed into the system via line 22. Thetemperature of this infeed is raised by transfer of the heat from thebrine blowdown and effluent distillate to approximately 217 F. whence itthen enters into the external heat source exchanger 24 which may beconveniently powered from the waste heat of a diesel engine 42 runningthe ship. The waste heat may be fed directly to the heat exchanger 24 orfirst through a heat recovery unit 44 which increases its operatingeffect. The infeed temperature is raised in heat exchanger 24 to 299 F.which, as will be appreciated, is rather a small differential. The powerrequirement for only a 12 F. raise in temperature is rather small andwill require only a portion of the ships waste heat.

On leaving the heat exchanger 24, the infeed enters into the reboiler asa spray and a portion flashes into vapor at approximately 227 F. Theremainder and unflashed infeed is mixed with the unspent brine exitingfrom the last stage at 237 F., where it is recirculated to the condensercoils as the condenser fluid for each of the chambers l4a-l4d. Thetemperature of this fluid increases as the flash vapor condenses so thatthe media exits from chamber 14a at 237 F. whence it passes throughheater 12 on its way to the flash chamber 10a. Simultaneously, the vaporproduced in the reboiler 26 is compressed by compressor 36 until itstemperature reaches 250 F. Such change in temperature, it will also beappreciated, does not require great compression and can be accomplishedeasily and simply with economical equipment. The compressed vapor is fedto the heater 12 where its heat is transferred to the brine condensingfluid to raise its temperature from 237 F. to approximately 245 F. as itenters the flash chamber 10a.

The compressor 36 may be driven in a variety of ways, such as by dieselor petrol engine, steam or gas turbine, or electric motor. in many casesdiesel engine drive will be most convenient, because the diesel can alsodrive an electric generator to produce the power needed to drive thepumps on the equipment. Further, the diesel will produce sufficientwaste heat from its exhaust gases and jacket water to operate heatexchanger 24. In this way the diesel fuel will be the only externalsupply of fuel, or heat or power, and this arrangement will beparticularly useful when a self-contained installation is required.

When a steam supply is available, the compressor could be turbine drivenor alternatively could be of the jet compressor type. The choice wouldbe dependent upon available steam conditions, and the quantity andpressure of process steam that could be used from the compressorexhaust, since only part of the jet compressor discharge would be neededby the feed heater.

The process described eliminates a number of the problems generallyassociated with high economy from distillation plants. Very few flashstages are required, reducing the complexity, cost and size of the mainvessel, and eliminating the subatmospheric stages. In orthodox flashunits it is necessary for good economy to have low temperature stagesoperative with small temperature differences, and this feature causesdifficult interstage flow and thermal equilibrium problems, which are,as has been seen, avoided here.

The device shown in FIG. 1 can be constructed of 4 flash chambers havinga total flash surface in flash chambers of approximately 9200 squarefeet, producing at the rate of 5.5 lbs. distillate per hour per squarefoot or a the total of I gallons per minute, all at a gained outputratio of better than to 1.

FIG. 2 indicates a modified version of the present invention which iscombined with certain subsidiary flash evaporation techniques to providea suitable land based system with small power requirement and highyield.

In the embodiment illustrated in FIG. 2 of the drawings, a source ofheat energy, such as a steam powered turbine 50 supplies heat through aconduit 52 to heat exchange coils 54 in a brine or feed solution heater56. The solution to be distilled is fed through coils 54 in the heater56 via line 58 to the flash chambers of a multistage flash evaporator60. The heater 56 is part of a generally larger heat exchange unit 62which includes a section 64 sealed from section 56 but through which thecoils 54 also extend.

The flash evaporator 60 includes a plurality of flash cham bers 60a-60dwhich operate at successively lower pressures and temperaturesproceeding from a high pressure stage 60a to a low pressure stage 60d.As the heated brine is introduced via line 58 successively through theflash chambers 60a-60d, a portion thereof flashes into vapor passingthrough lines 64 for condensation in heat recovery condensers 66a-66d.The unflashed brine exits from the low end flash chamber 60d throughline 68 into a relatively large heat reject flash chamber or reboiler70. Vapors produced in the heat reject flash chamber 70 are passed aslow pressure steam via line 72 to a compressor 74 which compresses thevapor, thereby causing an increase in its temperature. The compressedvapor is passed into the heater section 64 of the heat exchange unit 62to impart its heat to the media flowing through coils 54. Thiscompressed vapor consequently changes to distillate and is fed, via pipe76, to condensers 66a-66d to mix with the distillate formed therein.

The effluent brine not vaporized in reboiler 70 is passed via line 78,pump 80 and line 82 into the coils 84 of the condensing chambers 66a-66dwhere it acts as the condensing media for the vapor created in the flashchambers 60a-60d. The media passes counter to the flow of brine andexits from the high end condenser 66a into coils 54 of the heat exchangeunit via line 86. A portion of the brine effluent from reboiler 70 isblown down via line 88 branching off from pump 80 as required. A levelsensing device 90 is provided for this effect. Distillate exiting fromthe low end condenser 66d passes outwardly via pipe 92. Both blowdownand distillate pass independently and cooperatively through a brineheater and distillate cooler generally designated 94.

The brine heater and distillate cooler 94 comprises a feed heater 96 anda regenerative flash heater 98, both of which have evaporator andcondenser sections. The brine blowdown from pipe 88 passes first intothe evaporator of feed heater 96 thence through the evaporator of theregenerative flash heater 98 where some degree of flashing andproduction of distillate occurs. The residual brine exits via pipe 100and is dumped back into the sea. The distillate passing from the low endcondenser 66d through pipe 92 passes successively through the condensersections of the feed heater 96 and regenerative flash unit 98 and isfurther cooled and mixed with the distillate of those units finallyexiting via pipe 102 for collection as pure water.

The condenser sections of the regenerative flash unit 98 and the feedheater 96 are supplied with cooling media which itself is the incomingfeed supply of raw sea water for the entire system. Consequently, rawsea water is fed from the source via a pipe 104 through the condensingcoil 106 of a flashaerator device 108 thence via pipe 110 to thecondensing coil 112 of the regenerative flash unit 98, where on coolingthe distillate becomes warm. The raw sea water feed exits from theregenerative flash unit through a pump (not shown) via line 1 14 to befed as the distillant into the Flashurator 108 wherein it is flashed,condensed and withdrawn via line 116 to be used as desired.

If desired, the raw sea feed entering into the flashaerator 108 may betreated with acid injection via mechanism 118 whereby scale formation,etc. may be inhibited as is currently well known from reference to thepatents to Andrew Checkovitch U.S. 3,2l8,24l and 3,119,572.

The flashaerator device is, of course, employed primarily to deaerateand pretreat the incoming raw sea feed.

The unflashed raw sea feed is withdrawn from the flashaerator via pump120 and is fed as the condensing media to the coil 122 of the feedheater from whence it is fed via line 124 into the flash chamber of thereboiler 70 to mix with the brine exiting from the low end flash chamber60d. Feed water is thus continually entering the system to maintain thesystem supplied at equilibrium and constant cycle. If desired, anexternal heat source 126 is interposed in line 124 to provide any extraheat required by the system which is not furnished endothermically bythe system or by the turbine 50 heat supply.

Finally, provision is made via line 128 to remove, if desired, a portionof the reboiler vapor to use as live steam whenever such is required.For example, if the system is instalied in a resort hotel, the extrasteam may be used in the laundry facilities. Also, the compressor 74 isoperated by the turbine 50 through shaft 130 consequently reducing thepower requirement. Steam for the turbine can be obtained for normalsources and delivered via pipe 132.

The system shown in FIG. 2 operates and functions with similar resultsto the system shown in FIG. 1. It is believed unnecessary to provide theoperational parameters with regard to FIG. 2 since they would of coursebe comparable to those shown in FIG. 1. The system shown in FIG. 2 isadvantageous since its power supply can be obtained from the availablesources located either as a part of the site of installation or closelyadjacent thereto. Such auxiliary functions as acid treatment, sea feed,heating regeneration, etc. are also available with the system of FIG. 2.

It will now be seen that the objectives and advantages enumerated aboveare clearly obtainable with the present system which is susceptible to anumber of modifications and changes. Accordingly, it is intended thatthe preceding disclosure is by way of example only and that theinvention should be limited only to the appended claims.

What I claim is:

1. A flash evaporator comprising a plurality of stages operable atsuccessively lower pressures to establish a high pressure stage at oneend of said evaporator and a low pressure stage at the other endthereof, whereby heated feed solution introduced into said high pressurestage passes serially through said stages to said low pressure stageand-a portion of said feed solution flashes into vapor in each of saidstages; means to pass feed solution into said high pressure stage; meansto condense the vapors produced in said flash evaporator stages toprovide a distillate product; means defining a heat reject flash chamberto receive concentrated feed solution from said low pressure stage andheated raw sea water feed and produce steam, means for compressing saidsteam and heat recovery means for transferring the heat of said steam tosaid feed solution.

2. The evaporator according to claim 1 including means for withdrawingcompressed steam exhausted from said heat recovery means and mixing saidcompressed steam with the condensed vapors produced in said evaporator.

3. A flash evaporator according to claim 1 including heat generatingmeans and conduit means to sequentially pass said feed solution in heatexchange relationship with said heat generating means to said heatrejection means wherein a portion of said feed solution is converted tosteam in the low pressure stage of said flash evaporator condensingmeans and acts in said flash evaporator condensing means as thecondensing media and then passes to the high pressure stage flashevaporator to flash into vapor.

4. An evaporator according to claim 3 including means for withdrawingunflashed feed solution from said evaporator, means for withdrawingdistillate from said condensing means, both said withdrawing means beingin heat exchange relationship with the conduit means for passing feedsolution to the heat generating means whereby said feed solution may bepreheated.

5. A method of desalinating sea water comprising the steps of passingheated sea water feed solution serially through successively lowerpressure stages of a multistage flash evaporator to produce a vaporfraction and a brine fraction, condensing said vapor fraction to producea distillate and withdrawing said distillate passing said brine fractionto a boiler to convert a portion thereof along with a portion of heatedraw sea water feed into steam passing the remainder of said brinefraction of said heated sea water feed to waste, compressing said steamto increase its temperature, passing said compressed steam into heatexchange relationship with said feed solution to transfer the heatthereof to said feed solution.

6. The method according to claim 5 including the step of condensing saidcompressed steam and mixing the same with said condensed vapor fraction.

7. The method recited in claim 5 comprising the further steps ofpreheating raw sea water to form a part of said feed solution by passingit in heat exchange relation with said distillate product and with saidbrine portion discharged to waste and then treating said preheated rawsea water to remove corrosive agents therefrom.

8. The method recited in claim 7 in which said raw sea water ispreheated to temperatures in excess of 200 F.

9. The method recited in claim 7 in which said treating step comprisesinjecting acid into said preheated raw sea water to remove HCO ionstherefrom, and then deaerating the acid treated sea water to remove COand air therefrom.

10. The method recited in claim 9 in which said treated sea water ismixed with a brine fraction produced in said flash evaporator to formsaid feed solution.

2. The evaporator according to claim 1 including means for withdrawingcompressed steam exhausted from said heat recovery means and mixing saidcompressed steam with the condensed vapors produced in said evaporator.3. A flash evaporator according to claim 1 including heat generatingmeans and conduit means to sequentially pass said feed solution in heatexchange relationship with said heat generating means to said heatrejection means wherein a portion of said feed solution is converted tosteam in the low pressure stage of said flash evaporator condensingmeans and acts in said flash evaporator condensing means as thecondensing media and then passes to the high pressure stage flashevaporator to flash into vapor.
 4. An evaporator according to claim 3including means for withdrawing unflashed feed solution from saidevaporator, means for withdrawing distillate from said condensing means,both said withdrawing means being in heat exchange relationship with theconduit means For passing feed solution to the heat generating meanswhereby said feed solution may be preheated.
 5. A method of desalinatingsea water comprising the steps of passing heated sea water feed solutionserially through successively lower pressure stages of a multistageflash evaporator to produce a vapor fraction and a brine fraction,condensing said vapor fraction to produce a distillate and withdrawingsaid distillate passing said brine fraction to a boiler to convert aportion thereof along with a portion of heated raw sea water feed intosteam passing the remainder of said brine fraction of said heated seawater feed to waste, compressing said steam to increase its temperature,passing said compressed steam into heat exchange relationship with saidfeed solution to transfer the heat thereof to said feed solution.
 6. Themethod according to claim 5 including the step of condensing saidcompressed steam and mixing the same with said condensed vapor fraction.7. The method recited in claim 5 comprising the further steps ofpreheating raw sea water to form a part of said feed solution by passingit in heat exchange relation with said distillate product and with saidbrine portion discharged to waste and then treating said preheated rawsea water to remove corrosive agents therefrom.
 8. The method recited inclaim 7 in which said raw sea water is preheated to temperatures inexcess of 200* F.
 9. The method recited in claim 7 in which saidtreating step comprises injecting acid into said preheated raw sea waterto remove HCO3 ions therefrom, and then deaerating the acid treated seawater to remove CO2 and air therefrom.
 10. The method recited in claim 9in which said treated sea water is mixed with a brine fraction producedin said flash evaporator to form said feed solution.